1. Field of the Invention
The present invention relates to a breathing apparatus and, more particularly, to a breathing apparatus which can function as a gas supply apparatus for inhaling gases suitable for use in an air-free atmosphere, particularly under water.
2. Description of Related Art
A breathing apparatus for providing gases of inhalation including oxygen under water to a diver is known generally as an aqua lung, and such aqua lungs are currently employed extensively by divers and so on. The breathing apparatus comprises at least a mouth piece connected to the mouth of the diver or the like and a fresh air reservoir tank connected to the mouth piece.
By inhalation of air by the diver, the fresh air stored in the fresh air reservoir tank is supplied to the diver through the mouth piece. On the other hand, exhalation of air by the diver allows the exhaled air to be discharged from the mouth piece into a surrounding atmosphere, namely, into water.
A general type of the breathing apparatus is so designed as capable of employing the fresh air supplied from the fresh air reservoir tank only once as an air of inhalation. Hence, in order to accommodate a comparatively large amount of air, the fresh air reservoir tank is designed to be of a considerably large size. Nevertheless, the period of time that allows the diver or wearer to stay or work under water is limited to a comparatively short period of time.
From this standpoint, there have been proposed a variety of breathing apparatuses of a type capable of circulating and re-employing air exhaled by the diver or other wearers as air of next inhalation. In other words, it is possible to re-use the exhaled air as air of next inhalation as long as a content of carbon dioxide gas contained in the exhaled air would not exceed a predetermined value. Many breathing apparatuses of an exhalation circulating type have an exhalation reservoir tank which temporarily stores the air exhaled by the diver or other wearer through the mouth piece, as disclosed in, for example, Japanese Patent Unexamined Publication (kokai) No. 38,397/1975. Some breathing apparatuses are so designed as to remove carbon dioxide gas in the exhaled air by an adsorbing agent or the like prior to utilizing it as air of next inhalation as disclosed in, for example, Japanese Patent Unexamined Publication (kokai) No. 38,397/1975 and Japanese Patent Examined Publication (kokoku) No. 24,034/1984. Further, Japanese Patent Examined Publication (kokoku) No. 45,158/1977 proposes reutilization of the air exhaled at an initial stage of exhalation alone as air of inhalation, with the fact taken into consideration that the content of carbon dioxide gas is smaller in the initial stage of exhalation than in the later stage of exhalation to be made by the diver or wearer.
It is to be understood that the exhaled air containing carbon dioxide gas in the amount of approximately 7.5% or lower can be reutilized as air of inhalation. It can be noted that the air exhaled after a single act of breathing using fresh air as air of inhalation under one atmospheric pressure contains approximately 5% of carbon dioxide gas and approximately 15% of oxygen. On the other hand, the amount of oxygen to be used per a breath remains approximately constant regardless of the atmospheric pressure of the surrounding atmosphere, namely, the depth under water. This means that the rate of carbon dioxide gas to be contained in the air exhaled by one breath is reduced to a smaller extent as the depth under water becomes deeper. More specifically, the rates of carbon dioxide gas containing in the air exhaled when the air has been exhaled by one breath using fresh air as air of inhalation are about 2.5% under two atmospheric pressure, about 1.67% under three atmospheric pressure, and about 1.25% under four atmospheric pressure.
As is to be readily understood from the foregoing description, the present invention has been completed under circumstances as described hereinabove and has the object to provide a breathing apparatus so designed as to increase the number of times of re-employing the exhaled air as the depth under water becomes deeper.